The cutting power and the surface quality obtained with different abrasives, especially those that are carried on a flexible base, change with the degree of wear. During their use, the abrasive or grinding materials are progressively dulled so that the cutting depth is decreased until the grinding tool must be replaced. A great deal of experiment and development effort has been expended to create abrasives and grinding tools which provide improved material removal rates and increased lifetimes as well as improved surface cutting depths. A generally known disadvantage of these existing abrasive tools is the fact that the amount of material removed per unit time, i.e., the material removal rate, is initially high and then rapidly decreases so that in many cases the abrasive tool must be replaced after a relatively short time, even though the base on which the abrasive compound is held is still fully intact. Past efforts have been directed to changing the disposition of the abrasive grain in order to obtain more economical results.
The German Pat. No. 14 27 591 describes abrasive compounds which consist of a plurality of small, separated but bound abrasive elements which are embedded in a continuously yielding thermoplastic resinous mass which contains abrasive grain. After the production of a large mass of abrasive grain and organic, resin-like or rubber-like, heat hardenable plastics, the individual little grinding elements are formed and introduced into the larger mass.
The German Offenlegungsschrift No. 17 52 612 describes elastic abrasive grains in which the elastic binding material contains abrasive grains consisting of a plurality of individual grains and fixedly bound conglomerates.
From the German Offenlegungsschrift No. 23 48 338, it is known to place the abrasive grain in the abrasive grain layer as a plurality of hollow elements consisting of abrasive grain and binder.
The German Offenlegungsschrift No. 25 16 008 describes spherical grinding elements consisting of abrasive grains and a method for their production in which the carrier material is a thermoplastic material whose interior is substantially hollow and onto whose outer surface the grinding elements are molded.
The German Offenlegungsschrift No. 24 17 196 describes a method for producing abrasive elements on a base in which the abrasive belts consist of a carrier, the grinding particles, and base and covering materials. This publication indicates the advantages with respect to previously known grinding materials which consist of granulated grain and which are described in the German Pat. No. 14 27 591 and the German OS No. 17 52 612. According to this publication, the abrasive effort is increased, the grain and the carrier are utilized better but the abrasive grain acts somewhat as a compact abrassive grain of the same size, i.e., the cutting depths are substantially greater and less regular.
The German OS No. 16 94 703 describes a method for producing a resin-embedded grinding element in which abrasive particles are covered with silicone resin and the particles are then processed in a synthetic resin to a particular finished shape. The method is particularly distinguished by using corundum particles as the abrasive particles and these are provided with a silica coating prior to being covered with silicone resin. The silica coating may be applied by melting or sintering. The grinding compound obtained in this way is then treated with .gamma.-amino propyl ethoxy silane.
In the U.S. Pat. No. 2,194,472 (Jackson) the production of abrasive materials is described. The Jackson patent describes the manufacture of aggregate grains, the binders used to prepare the same and the binders used to fix the aggregate grains onto the flexible backing. At no point is there any mention of mixtures of different firmly bound agglomerates nor is this a decisive and critical step of the Jackson patent. Thus, only the production of agglomerate abrasive grains and their arrangement in the abrasive means are shown and all of the aggregates used in any given abrasive element have the same, that is identical, binder and thus the same strength.